Total wrist prosthesis and related methods

ABSTRACT

Disclosed is a wrist prosthesis, and methods for implanting same, the prosthesis comprising radial component having two sides, the first side comprising a stem and the second side comprising a concave dish; a carpal component having two sides, the first side comprising a stem, and the second side comprising a ball end, the ball end being connected to the carpal component through a neck, the neck being narrower than the diameter of the ball end; and a lunate component having two sides, the first side comprising a cavity adapted to receive said carpal component&#39;s ball end, and the second side comprising a convex surface adapted to engage said radial component&#39;s concave dish.

CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.15/468,223 filed Mar. 24, 2017, now U.S. Pat. No. 10,413,418, whichclaims the benefit of U.S. Provisional Patent Application Ser. No.62/312,869 filed on Mar. 4, 2016, the contents of which are incorporatedherein by reference.

FIELD OF INVENTION

The invention relates generally to prosthetic implants and in particularto prosthetic implants for use in a total wrist replacement procedure.

BACKGROUND OF THE INVENTION

As shown in FIG. 1, the human wrist consists of a cluster of 8 smallbones, the carpal bones, which flexibly connect the metacarpal bones 15,16, 17, 18, 19), located in the palm, with the ulna (3) and radius (4)located in the forearm. The carpal bones are generally arranged intodistal and proximal rows (5,6). The distal row of carpal bones consistsof the trapezium (7) trapezoid (8), capitate (9) and hamate (10) bones.The proximal row of carpal bones consists of the scaphoid (11), lunate(12), triquetrum (13), and pisiform (14) bones. In normal operation of ahealthy wrist, the articular surface of the radius (15) provides aconcave bearing surface which supports the articulation of the scaphoid(11) and lunate (12) as the wrist goes through its range of motion.

Due to injury, degenerative changes, disease (such as arthritis) orother conditions, a person may experience pain, discomfort, ordifficulty when operating the wrist through its range of motion. Knownprocedures for such wrist conditions are to fuse the scaphoid (11) andlunate (12) bones (and possibly other carpal bones) to themselves in a“four corner” fusion, or, in more extreme cases, total wristarthrodesis, which fuses the radius, some of the carpal bones and one ofthe metacarpal hones. While these procedures alleviate pain anddiscomfort, they greatly restrict the range of motion of the wristresulting in quality of life issues for the patient by limiting theutility of the wrist. In addition, in certain circumstances, because thebones in question are too deteriorated, or, in the case of fractures,not available, fusion is not possible.

In such circumstances, an available treatment is to replace all or someof the carpal bones with a prosthetic wrist in a procedure commonlyreferred to as a total wrist replacement Although previous efforts havebeen made to develop prosthetic wrists, they have met often withdisappointing results. Presently available wrist prostheses provide toolimited a range of motion, dislocate too easily, place too much stresson bones resulting in failure or fractures, cause complications such asinfections, and wear prematurely requiring additional surgeries duringthe patient's lifetime, among other flaws. In addition, the methodspresently used for implanting such prosthetic wrists often result inpoorly aligned joints and poor joint performance.

Accordingly, there is a need in the art for a prosthetic wrist, andassociated methods for implanting same, which provides a patient with arange of motion that approximates that of a healthy wrist, islong-lasting, provides adequate support for the remaining hand andforearm bones, and avoids many of the drawbacks of existing prostheticwrists.

SUMMARY OF THE INVENTION

A wrist prosthesis used in a total wrist replacement is disclosed. Thewrist prosthesis of the present invention replaces the proximal row ofcarpal bones and restores wrist function using three separatecomponents—a carpal component, a lunate component, and a radialcomponent. When assembled, the prosthesis attaches to the radius in theforearm and to the trapezoid (optionally), capitate, hamate(optionally), and third metacarpal bones in the hand. The threecomponents of the prostheses, when assembled provide for a wide range ofmovement between the radial and carpal components.

The radial component of the wrist prosthesis comprises a stem at itsproximal end for insertion into and attachment to the radius, and anapproximately semi-spherical concave bearing surface, or “dish”, at itsdistal end for engaging the lunate component. The carpal component ofthe wrist prosthesis comprises a stem and an alignment pin at its distalend for attachment to the capitate and third metacarpal bones, and aball end at its proximal end for engaging the lunate component. Someembodiments of the present invention additionally include holes forattachment of the carpal component to the trapezoidal and/or hamatebones.

Interposed between the radial and carpal components is the lunatecomponent which is comprised, in in its radial-facing side, of asemi-sphere which closely matches the geometry of the dish of the radialcomponent. The carpal-facing side of the lunate component is comprisedof a cavity that closely matches the geometry of the ball end of thecarpal component and allows the lunate component to “snap” onto the ballend of the carpal component. The center of the ball-shaped cavity in thelunate component is slightly offset proximally relative to the center ofthe outer spherical surface of the lunate component in order to providea “self-centering” characteristic to the arrangement of components asdiscussed in greater detail below.

The lunate component is manufactured from a durable yet resilientmaterial, such as ultra-high-molecular-weight polyethylene (“UHMWPE”).The carpal and radial components are manufactured from a high qualitysurgical-grade metallic alloy such as Cobalt-Chromium-Molybdenum(“CoCrMo”) well known for biomedical applications such as jointreplacements. The use of a polyethylene lunate component in cooperationwith the CoCrMo carpal and radial components provides various benefits,including (a) avoidance of any metal-on-metal interfaces between movingparts and known complications thereof; (b) self-lubrication of theinternal and external interfaces of the lunate component; (c) dampeningand absorption of impact loads on the prosthesis; and (d) exceptionaldurability.

Also disclosed is a method for performing a total wrist replacementusing the wrist prosthesis of the present invention. The method includesmaking an incision in the dorsal side of the wrist and exposing thecarpal bones and the articular surface of the radius. Next, the proximalrow of carpal bones, namely the scaphoid, lunate, triquetrum, andpisiform bones, are excised. An insertion hole, is next drilled in thearticular surface of the radius, optionally using a radial alignmenttool, and the stem of the radial component is inserted through theinsertion hole into the radius. Optionally, the articular surface of theradius may be prepared using a specialized shaping tool prior toinsertion of the radial component.

Two holes are next drilled, optionally using a carpal alignment tool;the first, longitudinally through the capitate bone and into the thirdmetacarpal bone to receive the stem of the carpal component, and thesecond into the central aspect of the capitate to receive the alignmentpin of the carpal component. Optionally, the capitate bone may beresized and prepared using a specialized shaping tool prior to insertionof the stem and alignment pin of the carpal component into the capitateand third metacarpal bones. Optionally, the carpal component be alsoattached to the hamate and trapezoidal bones through screws insertedinto attachment holes in some embodiments of the carpal component.

The carpal-facing cavity end of the lunate component is next “snapped”onto the ball end of the carpal component and the radial-facing end ofthe lunate component is buttressed against the dish end of the radialcomponent where it is allowed to “float.” Once all of the components aremanipulated into correct alignment to permit a range of motionapproximating that of a natural wrist, the incision is closed.

Although the invention is illustrated and described herein as embodiedin a wrist prosthesis, it is nevertheless not intended to be limited toonly the details shown, since various modifications and structuralchanges may be made therein without departing from the spirit of theinvention and within the scope and range of equivalents of the claims.Moreover, many of the principles and techniques discussed in thefollowing description can be applied to prostheses used in other jointsin the human anatomy such as the elbow, shoulder, hip, knee or ankle.

The construction of the invention, together with additional objects andadvantages thereof will be best understood from the followingdescription of the specific disclosed embodiments when read inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the bones of the human hand provided forreference only and known in the prior art.

FIG. 2 is an exploded orthographic view of the dorsal aspect of theradial, carpal and lunate components of a wrist prosthesis according tothe present invention.

FIG. 3 is an assembled view of the dorsal aspect of the radial, carpaland lunate components of a wrist prosthesis according to the presentinvention.

FIG. 4 is an orthographic distal end view of the radial component ofwrist prosthesis according to the present invention.

FIG. 5 is a side view of the radial component of a wrist prosthesisaccording to the present invention.

FIG. 6 is a proximal end view of the radial component of a wristprosthesis according to the present invention.

FIG. 7 is an orthographic view from the dorsal side of the carpalcomponent of a wrist prosthesis according to the present inventionwhich, optionally, includes two wings and attachment holes for thehamate and trapezoidal bones.

FIG. 8 is an orthographic view from the palmar side of the carpalcomponent of a wrist prosthesis according to the present invention.

FIG. 9 is an orthographic cross-sectional view of the carpal componentof a wrist prosthesis of FIG. 8 according to the present invention.

FIG. 10 is an orthographic view of the lunate component of a wristprosthesis according to the present invention.

FIG. 11 is a top view of the lunate component of a wrist prosthesisaccording to the present invention.

FIG. 12 is a side view of the lunate component of a wrist prosthesisaccording to the present invention.

FIG. 13 is a cross-sectional view of the lunate component of a wristprosthesis according to the present invention.

FIG. 14 is a cross-sectional assembled view of the carpal, lunate, andradial components of a wrist prosthesis according to the presentinvention.

FIG. 15 is a detail of a cross-sectional view of the assembled lunateand carpal components of a wrist prosthesis according to the presentinvention.

FIGS. 16A, 16B, and 16C are a sequence of views of the carpal, lunateand radial components illustrating their relative motion through anexemplary range of motion of a wrist prosthesis according to the presentinvention.

FIG. 17 illustrates an embodiment of the wrist prosthesis of the presentinvention implanted on a human hand with the surrounding skeletalanatomy represented as semi-transparent structures, shown for referenceonly.

FIG. 18 is an orthographic view of a radial drilling guide alignmenttool in accordance with the present invention.

FIG. 19 is an orthographic view of a radial dish guide tool inaccordance with the present invention.

FIG. 20 is an orthographic view of a radial dish reamer tool inaccordance with the present invention.

FIG. 21 is an orthographic view of a keel punch in accordance with thepresent invention.

FIG. 22 is an orthographic view of a capitate long axis guide inaccordance with the present invention.

FIG. 23 is an orthographic view of a stop reamer and planer inaccordance with the present invention.

FIG. 24 is an orthographic view of a capitate shaper in accordance withthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is an exploded orthographic view of the three components of awrist prosthesis (1) according to the present invention. As shown, thelunate component (300) is interposed between the radial component (100)and the carpal component (200). FIG. 3 shows an assembled view of thethree components from the same perspective.

Referring next to FIG. 4, shown is an orthographic representation of aradial component (100) according to the present invention. FIGS. 5 and 6respectively provide side and proximal end views of the radial component(100) and illustrate all details thereof. As shown in FIG. 4, the radialcomponent (100) is comprised of a proximal end (112) and a distal end(110). Stem (114) is projected in the direction of the proximal end andis adapted for insertion through the articular face of the radius andfor penetration into the medullary canal of the radius. The stem of theradial component may optionally include flutes (116) and/or a roughenedsurface finish, such as titanium plasma spray (“TPS”) coating, topromote post-operative bone growth for more permanent fixation afterhealing, and to prevent rotation of the component in the bone. Thedistal end of the radial component provides a distally facing concavedish (118) which is adapted to receive the convex portion (301) (shownin FIGS. 10, 11, 12 and 13) of the lunate component (300) upon assemblyof the prosthesis, as described in detail below.

The internal surface (120) of dish (118) is a substantially sphericallyconcave section which closely matches the geometry of the convex portionof the lunate component (300). In some embodiments of the radialcomponent (100), the spherical section defined by the internal surface(120) of dish (118) is less than half of a full sphere. The dishoptionally includes one or more lip extensions (122) which provideadditional rotational support area for the lunate component (300) whichcould be beneficial to provide for maximum flexing of the assembledprosthesis without dislocation of the lunate component (300).

To provide optimal alignment between the various components and thesurrounding anatomy, stem (112) is arranged with respect to dish (118)so that the longitudinal axis (124) of stem (114) forms an angle (126)of between approximately 60 and 80 degrees with respect to an imaginaryline (128) coplanar with the edge (130) of dish (118). In addition, stem(114) is offset laterally with respect to the center of dish (118) sothat longitudinal axis (124) of the stem (114) intersects the internalsurface (120) of dish (118) approximately tangentially. The external,bone contacting, surface (132) of dish (118) can optionally be,spherical or other shape that conforms to the articular face of theradius bone.

An additional optimal feature of radial component (100) is keel (134)which buttresses the junction between stem (114) and dish (118). Inaddition to providing structural support to dish (118), keel (134)minimizes the possibility of radial component (100) rotating aboutlongitudinal axis (124) after insertion into the radius. Furthermore,keel (134) acts as a wedge creating a tighter fit between the radiusbone and stem (114). Keel (134) may have a sharp edge to facilitatepenetration into the radius bone. Additionally, keel (134) may be ofsolid construction (as shown) or may be hollow, to provide a dual edgefor penetration of the radius bone and allows bone material to becomewedged in the inner space of keel (134).

Radial component (100), in one embodiment of the present invention, ismanufactured from a high quality surgical-grade metallic alloy, such asCoCrMo well known for biomedical applications such as jointreplacements. However, titanium or other metallic or non-metallicmaterials are also suitable for this component in alternativeembodiments.

Referring next to FIG. 7, shown is an orthographic representation of acarpal component (200) according to the present invention. FIG. 8 showsa side view of the carpal component (200) and FIG. 9 shows a crosssection of the carpal component (200).

With reference to FIG. 7, the distal end (201) of the carpal component(200) is comprised of a stem (204) which is adapted to penetrate intothe third metacarpal bone, preferably into the medullary canal of thethird metacarpal bone. The stem of the carpal component may optionallyinclude flutes (206) and/or a roughened surface finish to promotepost-operative bone growth for more permanent fixation after healing,and to prevent rotation of the component in the bone. The carpalcomponent also comprises alignment pin (208), in generally parallelalignment with stem (204), which is adapted to penetrate into thecentral aspect of the capitate bone. The purpose of alignment pin (208)is to minimize the possibility of rotation of carpal component (200)about longitudinal axis (210) of stem (204) after implantation. Carpalcomponent. (200) may also, optionally, include one or more wings (212T)(212H) which are positioned for anatomical alignment with the trapezoid(8) and hamate (10) bones and provide additional buttressing support forcarpal component (200) against said hones. Wings (212T), (212H) mayoptionally also include fastener holes (213T), (213H) for securing wings(212T) (212H) to the trapezoid (8) and hamate (10) bones using fasteners((215) in FIG. 9.

As best observed in FIG. 9, the stem (204) and alignment pin (208) ofthe carpal component terminate in cap (216) which is a concave structurewith respect to distal, end (202) of the carpal component. Alignment pin(208) terminates at or near the center (218) of the internal surface(220) of cap (216), while stem (204) is offset dorsally with respect toalignment pin (208) and terminates at the edge of cap (216). Theinternal surface (220) of cap (216) is adapted to contact, andoptionally encapsulate, the capitate bone upon implantation into thepatient's hand.

The proximal end (202) of carpal component (200) comprises ball end(222) with a diameter (223) which is connected to cap (216) through neckregion (224). Ball end (222) is a semi-complete (between 70% and 97% inthe disclosed embodiment but in any event greater than 50% of a sphere)sphere with its center in substantially direct longitudinal alignmentwith the center of cap (216) and the longitudinal axis (226) ofalignment pin (208). The ball end (222) and neck region (224) closelycomplement the geometry of corresponding features in the lunatecomponent (300) as discussed in more detail below.

Like radial component (100), carpal component (200), in one embodimentof the present invention, is manufactured from a high qualitysurgical-grade metallic alloy such as “CoCrMo” well known for biomedicalapplications such as joint replacements. However, titanium or othermetallic or non-metallic materials may also be suitable for thiscomponent.

Referring next to FIG. 10, shown is an orthographic representation of alunate component (300) according, to the present invention. FIGS. 11 and12 illustrate, respectively, top and side views of the lunate component(300). FIG. 13 is a cross sectional view, enlarged for clarity, of thelunate component (300) which, as evident from all views, is radiallysymmetrical.

As shown in FIGS. 10-13, the external surface (301) of lunate component(300), which is adapted to interface with the internal surface (120) ofdish (118) of radial component (100) (see FIGS. 4-6), approximatelydefines a half-sphere. However, alternative embodiments need notnecessarily define a half-sphere. Alternative embodiments of lunatecomponent (300) could define an external surface that is greater thanhalf of a sphere, or smaller than half of a sphere, it being understoodthat the greater the external surface is, the lower the possibility willbe of dislocation of the lunate component (300) with respect to radialcomponent (100).

Referring now to FIG. 10 through FIG. 13, lunate component (300)includes a cavity (302) comprised of a spherical region (304) and ashoulder region (306). The spherical region (304) of cavity (302) in allembodiments comprises more than a half-sphere so that the diameter ofthe “mouth” (308) of the spherical region (304) is narrower than thediameter (310) of the spherical region (304) and also narrower than thediameter (223) of ball end (222) of carpal component (200). Also, thediameter (310) of the spherical region (304) is somewhat larger than thediameter (223) of the ball end (222) of carpal component (200) as toprovide sufficient clearance for the ball end of the carpal component torotate freely within the spherical region (304). The shoulder region(306), in turn, gradually widens away from the spherical region (304) toform a funnel-like toroidal structure atop the lunate component. Thespherical and shoulder regions of cavity (302) closely match thegeometry of the ball end (222) and neck region (224) of carpal component(200) (See FIGS. 7-9).

Lunate component (300) is manufactured from a durable yet resilientmaterial, such as “UHMWPE”, or other surgical grade resilient material.

Referring next to FIG. 14 and FIG. 15 therein are shown cross-sectionalviews of the carpal (200), lunate (300) and radial (100) components ofthe wrist prosthesis (1) of the present invention, upon assembly. Aswill be noted, since the mouth (308) of spherical region (304) of cavity(302) of the lunate component (300) is narrower than the diameter (223)of the ball end (222) of the carpal component (200), in order toassemble the carpal and lunate components, ball end (222) must be forcedinto cavity (302) until it snaps into place. That is, the lunatecomponent is briefly deformed but immediately snaps back to its originalshape retaining the ball end (222) within its cavity (302). Once inplace, however, the lunate component is held securely with respect tothe carpal component but the two components freely rotate and swivelwith respect to each other.

Shown in FIG. 15 is a detail of the cross sectional view of theassembled lunate component (300) and carpal component (200). As is shownin this view, the center (402) of ball end (222) and the center (400) ofthe external surface (301) of the lunate component (300) are notcoincident. Instead the center (402) of ball end (222) is offsetproximally relative to the center (400) of the external surface (301) inthe proximal-distal direction by a distance (404) of between 1 and 10mm. This offset achieves two objectives. First, it minimizes the chanceof the lunate and carpal components accidentally separating. Byembedding cavity (302) deeper into the lunate component (300), theleverage caused at the limits of flexion will not cause the ball end tobe dislodged. Second, the offsets provides the lunate-carpal couplingself-centering characteristics which ensure that through a series offlexions of the prosthesis the lunate component will be urged towardsits neutral position, instead of remaining in an extreme position.

The self-centering characteristic of the lunate component is due to thefact that when the center (402) of the ball end (222) is offsetproximally with respect to the center (400) of external surface (301) ofthe lunate component, the moment imparted on the lunate component by thenatural normal load forces on the wrist is always greater, and in thecenter-biased direction, than the moment imparted on the lunatecomponent by rotational frictional forces, which is non-centering. Thegreater the offset distance (404) between the two centers (400, 402),the greater the imbalance between the two moments and the stronger theself-centering tendency.

Referring again to FIG. 14, the lunate component (300), “floats” on topof the dish (118) of the radial component (100) and similarly freelyrotates and swivels about the center of the dish (118). The two separaterotational pairings (carpal-lunate and lunate-radial) are independent ofeach other providing exceptional freedom of movement and flexibility inthe prosthesis. Moreover, the interface between the UHMWPE and CoCrMo isnaturally self-lubricating and provides exceptional smoothness andcomfort in rotational and swiveling motions. It is noted, however, thatthe frictional torque between the lunate component (300) and the dish(118) of the radial component (100) is greater than the frictionaltorque between the ball end (222) of the carpal component (200) and thelunate component (300). Therefore, rotation will occur primarily in thecarpal-lunate interface. Lunate-radial rotation will generally occurafter a limit of rotation has been reached in the carpal-lunateinterface, such as when the neck region (224) of the carpal component(200) comes into contact with the shoulder region (306) of the lunatecomponent (300).

Shown in FIGS. 16A, 16B, and 16C is an exemplary sequence of relativemovements between the carpal, lunate and radial components. Beginningwith FIG. 16A, the carpal (200), lunate (300) and radial (100)components are in a neutral position. As upward force “F” is applied tothe carpal component (200), the carpal component begins to rotate in aclockwise direction with respect to the lunate component (300). Becausethe frictional torque between the carpal and lunate components (200,300) is less than that between the lunate and radial components (300,100), there will be very little, if any, relative motion between thelunate (300) and radial (100) components at this phase.

This movement continues until, as shown in FIG. 16B, neck region (224)of the carpal component (200) comes into contact with shoulder region(306) of the lunate component (300). At this point, if upward force Fcontinues to be applied to carpal component (200), the carpal and lunatecomponents will begin to rotate together relative to the radialcomponent (100) in a clockwise direction about the center (400) of theof the external surface (301) of the lunate component (300) as shown inFIG. 16C.

If a downward force is applied at this point to carpal component (200),a similar sequence (not shown) will be repeated in the oppositedirection with relative counterclockwise motion first occurring betweenthe carpal and lunate components (200, 300) until a limit of motion isreached and then with the carpal and lunate components (200, 300) movingin tandem in the counterclockwise direction relative to the radialcomponent (100).

Illustrated in FIG. 17 is an embodiment of the disclosed wristprosthesis (1) shown with the surrounding skeletal anatomy forreference. Shown in dotted contour and transparent for clarity are thebones wherein the wrist prosthesis is implanted: The radius (4) thethird metacarpal (17), the trapezoid (8), the lunate (9) and the hamate(10). The proximal row of carpal bones, namely the scaphoid, lunate,triquetrum, and pisiform bones are not shown, having been excisedsurgically as further explained below.

In addition to the above-disclosed prosthetic wrist, a method forsurgically implanting same on a human patient is disclosed. The methodincludes the following basic sequence of steps:

An incision is made longitudinally on the dorsal side of the affectedwrist and skin, muscle and tendons are retracted to expose the carpalbones and the distal end of the radius, including its articular surface.

The proximal row of carpal bones, namely the scaphoid, lunate,triquetrum, and pisiform bones, are excised, exposing the proximalarticular surface of the second row of carpal bones, primarily thecapitate and hamate bones.

Each of the lunate (300), carpal (200) and radial (100) components areoptionally provided in one or more, sizes. The proper size of eachcomponent is dictated by the patient's anatomy. Optionally, this propersizing may be accomplished during surgery by selecting andpre-assembling various sizes of equivalent modeling versions (not shown)of each of those components.

An insertion hole is drilled near the center of the articular surface ofthe distal radius, optionally using a radial sizing/alignment tool forprecise location of the hole. The optional radial sizing/alignment tool(500) is shown in FIG. 18. The radial sizing/alignment tool (500)includes visual cues (502, 504, 506) which can be matched—to the palmarand dorsal corners of the radio-ulnar joint, and the tip of the radialstyloid, on the articular surface of the distal radius. Once the tool isproperly placed, the center of circle (508) marks the spot where theradius should be drilled to insert the stem (114) of the radialcomponent (100). The drilled hole is then reamed to the proper size.

The stem (114) of the radial component (100) is then inserted throughthe previously drilled hole into the radius until the leading tip ofkeel (134) contacts the articular surface. The precise orientation ofthe radial component (100) may be optimized prior to insertion by usingan optional radial dish guide tool (550) shown in FIG. 19. The stem(552) of the radial dish guide tool (550) is inserted into the holedrilled into the articular surface of the radius and is then rotateduntil the outer edge of ring (55) is centered on the articular surfaceof the radius. A k-wire (not shown) is then inserted through orifice(556) and the radial dish guide tool (550) is removed. The location ofthe k-wire marks the center of dish (118).

Optionally, the articular surface of the radius may be prepared toreceive the radial component (100) by shaping the articular surface ofthe radius to match the external surface (132) of the dish (118) of theradial component (100). This is accomplished by using the optionalradial dish reamer tool (570) shown in FIG. 20. The radial dish reamertool orifice (572) is inserted over the k-wire placed in the previousstep and the articular surface of the radius is then reamed until thecutting flutes (574) of the radial dish reamer tool (570) are flush withthe radial edge of the articular surface of the radius. The k-wire canthen be removed from the articular surface of the radius.

The radial component (100) is then tapped into the radius with asurgical mallet until external surface (132) of the dish (118) of theradial component (100) makes full contact with the articular surface ofthe radius, further embedding stem (114) and keel (134) in the radiusand locking the radial component in place. The articular surface of theradius may optionally be prepared for insertion of keel (134) by usingoptional keel punch (580) shown in FIG. 21. This step concludes theplacement of the radial component (100).

Next, the long axis of the capitate bone is identified for placement ofthe carpal component (200). This may optionally be accomplished by usingthe capitate long axis guide (600) shown in FIG. 22. The guide (600) isplaced on the third metacarpal bone and slid distally until ring (602)is flush with the proximate pole of the capitate bone. Next, a k-wire isinserted through orifice (604) of the guide and into the capitate bone.Guide (600) is then removed leaving the k-wire in place. Alignment ofthe k-wire may be confirmed using fluoroscopy.

As needed, the capitate bone may be shortened by using the optional stopreamer (620) shown in FIG. 23 over the k-wire inserted in the previousstep. Next, the capitate bone is optionally prepared to receive thecarpal component (200) by shaping the proximal articular surface of thecapitate bone to match the internal surface (220) of cap (216) of thecarpal component (200). This can be accomplished by using the optionalcapitate shaper (640) shown in FIG. 24. The orifice (642) of thecapitate shaper (640), attached to a drill (not shown), is inserted overthe k-wire placed in the previous step. The blades (644) are then usedto shape the capitate bone to receive the carpal component (200).

Next, a first hole is drilled into the capitate using the previouslyinserted k-wire. The first hole is reamed to the appropriate size toaccept the alignment pin (208) of the carpal component and the k-wire isremoved.

A second hole is next drilled into the third metacarpal bone inlongitudinal tangential alignment with the dorsal aspect of thecapitate. The offset between the first and second holes matching thedistance between the stem (204) and alignment pin (208) of the carpalcomponent (200).

The alignment pin (208) and stem (204) of the carpal component (200) arethen inserted into the first and second holes respectively until stem(204) is in the medullary canal of the third metacarpal bone and cap(216) makes contact with the capitate bone.

The carpal component is then tapped into the capitate bone with asurgical mallet until the capitate bone is fully encapsulated by cap(216). If the carpal component is equipped with optional wings (212H),and/or 212T), the wings should be positioned directly against the hamateand/or trapezoidal bones and can be secured using screws (251) throughholes (213H, and/or 213T). Any gap between wings (212H, and/or 212T) andthe hamate and/or trapezoidal bones may be filled with bone graft.

The lunate component (300) is next “snapped” onto the ball end (222) ofthe carpal component (200) through cavity (302) and the surgeon verifiesthat the carpal and lunate components are securely attached but freelyswivel and rotate with respect to each other.

The external surface (301) of the lunate component is then buttressedagainst the dish (118) of the radial component (100) where it is allowedto “float.” Again, the surgeon verifies that the lunate component (300)is free to rotate and swivel on the dish (118) of the radial component(100).

The surgeon then tests for correct operation of the prosthesis bymanipulating and flexing the patient's hand through the range of naturalwrist motion and observing proper alignment.

After any remaining alignment issues are corrected and satisfactoryrange of motion is achieved by the surgeon the incision is closed usingstandard surgical techniques.

Although described above connection with a prosthetic wrist, thesedescriptions are not intended to be limiting, as other prosthetic jointscan be made in accordance with the description herein, and applied todifferent parts of the body such as elbows, shoulders, hips, knees andankles. As such, although the invention is illustrated and describedherein, various modifications and structural changes may be made thereinwithout departing from the spirit of the invention and within the scopeand range of equivalents of the claims.

We claim:
 1. A wrist prosthesis comprising: a radial component havingtwo sides, the first side comprising a stem and the second sidecomprising a concave dish; a carpal component having two sides, thefirst side comprising a stem, and the second side comprising a ball end,the ball end being connected to the carpal component through a neck, theneck being narrower than the diameter of the ball end; and a lunatecomponent having two sides, the first side comprising a cavity adaptedto receive said carpal component's ball end, and the second sidecomprising a convex surface adapted to engage said radial component'sconcave dish; said lunate component adapted to freely rotate withrespect to at least one of said radial component and said carpalcomponent about a longitudinal axis extending through the center of saidball end and substantially parallel to said stem of said carpalcomponent.
 2. A wrist prosthesis according to claim 1 wherein said stemof said carpal component is adapted for rigid engagement with one ormore carpal and/or metacarpal bones.
 3. A wrist prosthesis according toclaim 1 wherein said stem of said radial component is adapted for rigidengagement with a radius bone.
 4. A wrist prosthesis according to claim1 wherein the lunate component further comprises a mouth connected tothe cavity of the lunate component, the mouth being smaller in diameterthan the diameter of the cavity.
 5. A wrist prosthesis according toclaim 1 wherein the ball end of the carpal component is adapted to snapinto, and be retained by, the cavity of the lunate component.
 6. A wristprosthesis according to claim 5 wherein said lunate component comprisesa resilient material.
 7. A wrist prosthesis according to claim 1 whereinsaid carpal component further comprises an alignment pin substantiallyparallel to said stem of said carpal component.
 8. A wrist prosthesisaccording to claim 7 wherein said alignment pin is adapted for rigidengagement to a capitate bone.
 9. A wrist prosthesis according to claim1 wherein said carpal component further comprises one or more wings,each positioned for anatomical alignment with an individual carpal bone.10. A wrist prosthesis according to claim 9 wherein at least one of saidwings comprises a fastener hole.
 11. A wrist prosthesis according toclaim 10 wherein said fastener hole is threaded.
 12. A wrist prosthesisaccording to claim 1 wherein an axis extending along the length of thestem of said radial component is not normal to an imaginary linecoplanar with edge of the concave dish of the radial component.
 13. Awrist prosthesis according to claim 1 wherein an axis extending alongthe length of the stem of said radial component is approximatelytangential to the concave dish of the radial component.
 14. A method forsurgically implanting a wrist prosthesis comprising the steps of:rigidly engaging in the radius bone of a patient a radial componenthaving two sides, the first side comprising a stem and the second sidecomprising a concave dish, by embedding said stem in said radius bone;rigidly engaging in a carpal or metacarpal bone of a patient a carpalcomponent having two sides, the first side comprising a stem, and thesecond side comprising a ball end, the ball end being connected to thecarpal component through a neck, the neck being narrower than thediameter of the ball end, by embedding said stem in said carpal ormetacarpal bone; attaching to said carpal component's ball end a lunatecomponent having a cavity adapted for such attachment; and engaging saidlunate component with said concave dish of said radial component througha convex surface on said lunate component adapted for such engagement;wherein said lunate component is adapted to freely rotate with respectto at least one of said radial component and said carpal component abouta longitudinal axis extending through the center of said ball end andsubstantially parallel to said stem of said carpal component.
 15. Themethod for surgically implanting a wrist prosthesis according to claim14 wherein the lunate component further comprises a mouth connected tothe cavity of the lunate component, the mouth being smaller in diameterthan the diameter of the cavity.
 16. The method for surgicallyimplanting a wrist prosthesis according to claim 14 wherein the ball endof the carpal component is adapted to snap into, and be retained by, thecavity of the lunate component.
 17. The method for surgically implantinga wrist prosthesis according to claim 16 wherein said lunate componentcomprises a resilient material.